从从转义字符到字符常量的过程，是计算机内部的变化，即如何通过一个对应的数字如八进制转化到一个字符?
计算机网络中，有关于通信和转义说明的很清楚，为什么需要转义，和信息的表现形式。属于基础课程
\a
Bell (alert)
\b
Backspace
\f
Formfeed
\n
New line
\r
Carriage return
\t
Horizontal tab
\v
Vertical tab
\'
Single quotation mark
\"
Double quotation mark
\
Backslash
\?
Literal question mark
\ooo
ASCII character in octal notation
\xhh
ASCII character in hexadecimal notation
\xhhhh
Unicode character in hexadecimal notation if this escape sequence is used in a wide-character constant or a Unicode string literal.
For example, WCHAR f = L'\x4e00' or WCHAR b[] = L"The Chinese character for one is \x4e00".
这么的转义字符定义。。不管你是十进制，八进制和十六进制，对于计算机都是0和1，
int n = '\123';
printf("%c\n",n);